The present invention disclosed herein relates to a substrate processing apparatus, and more particularly, to a buffer unit in which a photomask temporarily stays, a substrate processing apparatus, and a substrate processing method.
Photomasks are quartz or glass substrates covered with a pattern corresponding to a minute semiconductor circuit. For example, a chrome thin layer applied on an upper layer of a transparent quartz substrate is etched to form a pattern corresponding to a semiconductor integrated circuit or a liquid crystal display (LCD) circuit. The size of the pattern is 1 to 5 times greater than that of the semiconductor integrated circuit or the LCD circuit. A minute pattern of a photomask is formed on a substrate through a photolithography process. In a photolithography process, a photoresist is uniformly applied on a substrate, then, a scale-down projection/exposure process is performed using a pattern of a photomask and an exposure device such as a stepper, and then, a development process is performed to form a two dimensional photoresist pattern.
When a foreign substance is attached to a photomask, the foreign substance scatters or absorbs light during an exposure process, so as to degrade optical resolution, thereby causing a significant defect in a pattern formed on a substrate. Thus, a pellicle as a protective member is installed on a photomask during an exposure process in order to protect the photomask from foreign substances. The pellicle is disposed at a certain height over a pattern of the photomask such that even though a foreign substance is attached to the pellicle, the foreign substance does not affect an image formed on a substrate during the exposure process.
Photomasks may be cleaned in a wet cleaning apparatus using a chemical such as a sulfuric peroxide mixture (SPM). When a photomask to which a foreign substance such as an adhesive is attached is used in an exposure process, as the exposure process is performed, the foreign substance may be gradually grown as a haze defect by catalysis energy of light. Since such growing haze defects cause undesirable pattern transfer, it is needed to effectively remove a foreign substance such as an adhesive from a photomask.
When a photomask is loaded into a photomask cleaning apparatus, a cleaning target surface of the photomask (a pattern surface thereof) may be oriented downward (reversed). To this end, photomask cleaning apparatuses include a device for reversing a photomask. Since such a reversing device is disposed within a photomask cleaning chamber, the reversing device is susceptible to corrosion due to chemical fumes, and particles generated from a driving part may contaminate a photomask and the inside of the photomask cleaning chamber.